Acrylic modified anionic water dispersible styrene hydroxyethyl (meth)acrylate copolymers

ABSTRACT

This invention provides a graft copolymer of at least one acrylic monomer and a random copolymer of a styrene and hydroxyethyl (meth)acrylate, in which at least about 8 percent of the total weight of said graft copolymer is derived from acrylic acid, methacrylic acid, or both. It also provides anionic aqueous dispersions of such graft copolymers and coating compositions containing them.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is concerned with acrylic modified copolymers of styreneand hydroxyethyl (meth)acrylate.

2. Description of the Prior Art

Insofar as is now known, the polymers of this invention have not beenproposed.

SUMMARY OF THE INVENTION

This invention provides a graft copolymer of at least one acrylicmonomer and a random copolymer of a styrene and hydroxyethyl(meth)acrylate, in which at least about 8 percent of the total weight ofsaid graft copolymer is derived from acrylic acid, methacrylic acid, orboth. It also provides anionic aqueous dispersions of such graftcopolymers and coating compositions containing them.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The main backbone chain of the graft copolymers of this invention arerandom copolymers of a styrene and hydroxyethyl (meth)acrylate. Styreneis a preferred monomer, but other styrene monomers are contemplated andcan be used, such as α-methylstyrene, p-methylstyrene, dimethylstyrene,ethylstyrene, chlorostyrene, dichlorostyrene, and the like. The amountof hydroxyethyl (meth)acrylate in the random copolymer will be betweenabout 20 percent and about 30 percent of the weight of the copolymer,with the balance being a styrene.

The copolymerization is carried out by any of the means well known inthe art. Typically, the monomers are dissolved in a suitable solvent,such as methyl ethyl ketone, methoxyethanol, ethoxyethanol, and thelike. The copolymerization can be carried out under free radicalconditions using a suitable free radical initiator, such as t-butylperbenzoate or benzoyl peroxide. The temperature used is the activationtemperature of the catalyst.

The random copolymer is grafted with at least one acrylic monomer.Various acrylic monomers and monomers copolymerizable therewith can beused. In order to provide sufficient free carboxyl groups to render thegraft copolymer water dispersible, however, at least about 8 percent ofits weight must be acrylic acid or methacrylic acid moieties. Theacrylic monomers can all be acrylic acid or methacrylic acid or it canbe a mixture of acrylic monomers or of acrylic monomers and othermonomers polymerizable therewith, provided that sufficient acrylic ormethacrylic acid is used to amount to at least about 8 percent of thetotal weight of the graft copolymer. Non-limiting examples of utilizableacrylic monomers are acrylic acid, methacrylic acid, methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, propylacrylate, propyl methacrylate, butyl acrylate, butyl methacrylate,hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, acrylonitrile, methyacrylonitrile acrylamide,methacrylamide, and monomers copolymerizable therewith, such as styrene,p-methylstyrene and lower monoolefins.

The graft copolymerization can be carried out by polymerizing theacrylic monomer or monomers in a solution of the random copolymerbackbone resin under free radical conditions. The solvent, free radicalinitiator, and temperature can be as described hereinbefore for therandom copolymer preparation.

In forming a coating composition containing the acidic graft copolymerresin, the resin is neutralized with a tertiary amine, ammonia, orammonium hydroxide to a pH about 7.0 to about 9.0. Typical aminesutilizable include triethylamine, tripropylamine, dimethylethanolamine,diethylethanolamine, dimethylethylamine, and methyldiethylamine.

In the finished coating composition, the resin solids content will beabout 10 to about 40 weight percent. The volatile system (includingamine, ammonia, or ammonium hydroxide) will be between about 90 weightpercent and about 60 weight percent of the finished coating composition,preferably about 75-85 weight percent. About 65 to 90 weight percent ofthe volatile system will be water and the balance (35 to 10 weightpercent) will be organic volatile solvents, including amine, ammonia, orammonium hydroxide. Preferably, the ratio of water to organic volatileswill be about 70:30 to 80:20 in the volatile system. Each component ofthe solvent system will be present in between about one weight percentand about 20 weight percent of the weight of the final composition. Atypical and preferred solvent system is defined in the working examples.

The coating composition will contain a cross-linking agent, such as anaminoplast or one of the well known diisocyanates such as tolylenediisocyanates. The preferred material used to thermoset the coating isconventional aminoplast cross-linking agent. Such agents are well knownin the art. There can be used any of the thermosetting alkylatedaminoplast resins, such as the urea-aldehyde resins, themelamine-aldehyde resins, the dicyandiamide-aldehyde resins and otheraminoplast-aldehyde resins such as those triazine resins produced by thereaction of an aldehyde with formoguanamine, ammeline,2-chloro-4,6-diamino-1,3,5,-triazine,2-phenyl-p-oxy-4,6-diamino-1,3,5-triazine,6-methyl-2,-4-diamino-1,3,5-triazine; 2,4,6-trihydrazine-1,3,5-triazine,and 2,4,6-triethyltriamino-1,3,5-triazine. The mono-, di-, or triaralkylor mono, di-, or triaryl melamines, for instance,2,4,6-triphenyltriamino-1,3,5-triazine can be used. Also utilizable arebenzoguanamine and hexamethoxymethyl melamine. As aldehydes used toreact with the amino compound to form the resinous material, one may usesuch aldehydes as formaldehyde, acetaldehyde, crotonic aldehyde,acrolein, or compounds which engender aldehydes, such ashexamethylenetetramine, paraldehyde, paraformaldehyde, and the like. Itis preferred to use an aminoplast that is water soluble. The amount ofcross-linking agent used is generally between about 15 weight percentand about 40 weight percent, based on total resin solids.

The coating composition of this invention is primarily useful forcoating aluminum, tin plated steel, pretreated metals, steel, and metalscoated with the same or different resin composition (i.e., a secondcoat). The coating composition can be used, however, for coating othersubstrates such as wood, paper and leather. The most preferred anduseful use of the coating composition is for coating of cans, coilstock, and fabricated metal. Coating can be done by any coatingprocedure well known to those skilled in the art including directroll-coating, electrodeposition, spraying, flow coating and the like.After coating the substrate, the coating is baked for about one minuteto about 30 minutes at between about 120° C. and about 260° C.

EXAMPLE 1

A five liter round bottom flask was charged with 1000.0 g. of Cellosolvewhich was subsequently heated to 125° C. in a nitrogen atmosphere. Amixture of 1500.0 g. of styrene, 500.0 g. of hydroxyethyl methacrylateand 100.0 g. of t-butylperbenzoate was added dropwise over a three hourperiod. After an additional hour at 125° C., the reaction flask wasdischarged. The resulting product was determined to contain 67.6 percentnon-volatile polymer by heating a sample for two hours at 150° C. The Mnwas 5,728 and Mw was 15,100.

EXAMPLE 2

A two liter resin kettle was charged with 251.0 g. of the copolymer ofstyrene and hydroxyethyl methacrylate from Example 1 and 39.0 g. ofCellosolve. It was heated to 110° C., under nitrogen at which time asolution of 57.5 g. of methacrylic acid, 100.0 g. of styrene, 167.5 g.of butyl acrylate, and 23.0 g. of benzoyl peroxide was added dropwiseover a three hour period. The reaction mixture was held at 110° C. forone hour and then cooled to 90° C. whereupon 3.3 g. of additionalbenzoyl peroxide was added. After an additional hour at 90° C., 53.6 g.of dimethylethanolamine and 53.6 g. of deionized water were added.Subsequently, 936.4 g. of deionized water was added over a two hourperiod. The resulting aqueous dispersion (pH=8.36, Brookfieldviscosity=360 cps.) was determined to contain 30.6 percent non-volatilematerial (2 hrs. @ 150° C.) with an acid number of 83.6 (on solids).

EXAMPLES 3 through 5

Using the process described in Example 2, three resins and aqueousdispersions thereof were prepared. The polymer used was the copolymer ofExample 1. The weight percent of the resin components and the finalconstants of each dispersion are set forth in the Table.

                  TABLE                                                           ______________________________________                                        Components, Wt. %                                                             Ex.  Poly-                      %    Visc.,                                   No.  mer     MAA.sup.1                                                                             Styr..sup.2                                                                         BA.sup.3                                                                           NV   (cps) A.N. ph                            ______________________________________                                        3    50.0    11.5    20.0  18.5 32.0  40   88.1 8.33                          4    35.0     9.5    15.0  40.5 30.4 160   73.1 8.26                          5    50.0    11.5     9.0  29.5 30.7 140   83.2 7.98                          ______________________________________                                         .sup.1 Methacrylic Acid                                                       .sup.2 Styrene                                                                .sup.3 Butyl Acrylate                                                    

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchmodifications and variations are considered to be within the purview andscope of the appended claims.

What is claimed is:
 1. A graft copolymer of an acrylic monomer ormonomers or of acrylic monomer or monomers and other monomerscopolymerizable therewith ion a backbone comprising a random copolymerof a styrene and between about 20 weight percent and about 30 weightpercent of the random copolymer of hydroxyethyl (meth)acrylate, in whichat least about 8 percent of the total weight of said graft copolymer isderived from acrylic acid, methacrylic acid, or both.
 2. The graftcopolymer of claim 1, wherein the styrene in said random copolymer isstyrene.
 3. The graft copolymer of claim 2, wherein said acrylicmonomers and other monomers copolymerizable therewith are methacrylicacid, styrene, and butyl acrylate.